DescriptionThis species of gimnosomate is usually 10 to 15 mm long, although there are citations of specimens living in cold waters that reach more than 5 cm long. The body shape is elongated, with a distinctive anterior zone or head, a neck, the body and a small rear zone. The body is translucent but the pink-orange viscera give the animal these colors. The head is broad and has two lobes, with a mouth opening in a groove between the two lobes and where several round bumps (buccal cones) could be observed. The head has a pair of short retractile rhinophores and continues with a sort of retractile neck. The dominant color of the head and neck is pink. The body is elongated but contractile, with a rounded anterior margin and becoming thinner towards the back. In the middle section of the body there is a slightly apparent constriction with ciliated cells forming a ciliated crown all around the body. Inside the body there could be seen, by transparency, the reddish gut and other creamy-white viscera that occupy two-thirds of the body space while the final third is empty, with no viscera. In the head and body there are semitransparent spherical granules, mainly concentrated in the anterior region of the body. The ventral area of ​​the body has two thin, semitransparent, longitudinally striated, swimming fins attached, also contractile. The foot is a small ventral surface located between the two triangular fins and has two lobulations somewhat wider. The rear end of the body or caudal cone has a widened anterior lip and its cells have long cilia in constant motion. Inside the caudal cone there are also bright spherules.

BiologyClione limacina is the most abundant gimnosomate in the surface plankton of temperate and polar waters, becoming an important food source for whales and certain fishes. It is a monophage species that feeds specifically of thecosomata of the genus Limacina: L. helicina in the cold Arctic and Antarctic waters and of L.retroversa in temperate waters of both hemispheres. They capture their food by evaginating their buccal cones and holding their preys with them. Inside the body there are abundant lipid granules, visible as bright spherules, synthesized by the animal, that are very important as an energy resource for reproduction and survival during the winter months, where there is little food. The mating of two individuals of C. limacina is achieved by joining their ventral parts, and fertilization is reciprocal. Some authors suggest that their lifespan is no less than two years.

Etymology

Clione. From Greek “kleio”, Ocean’s daughter and sister of Beroe.

Limacina. Diminutive of Limacia. Slug, slimy.

DistributionThis gimnosomate has a polar distribution. It is considered that there are two subspecies, C. limacina limacina living in the northern hemisphere (both Atlantic and Pacific), between North pole and 40°N and subspecies C. limacina antarctica living in the southern hemisphere that until recently was considered a separate species (Clione antarctica). In the Iberian Peninsula has been cited in the Portuguese coast and in Catalonia it has been found over the continental shelf, off the Garraf coast.